While a demand for increase of the capacity and the speed of data processing is increasing, it is pointed out that a limit exists in the speeding up, power saving and downsizing in future computers/integrated circuits. In order to break down the limit, implementation of a device/system in which optical interconnections and electronic circuitry are integrated together is desired together with development of technical fields that use a new electronic phenomenon in semiconductors.
In such a situation as described above, attention gathers to Si photonics of producing an optical circuit on an SOI (Silicon on Insulator) substrate using a silicon (Si) microfabrication technology, and development of an optical interconnect technology characterized in speeding up, power saving and downsizing is performed actively.
Incidentally, since Si itself does not include a light emitting mechanism, in the optical interconnect technology that uses the Si photonics, it is investigated to input external light to an optical waveguide that configures an optical circuit on an SOI substrate.
However, a core of an optical waveguide by Si microfabrication has, as a size thereof, a width of, for example, approximately 450 nm in order to keep a single mode of propagation light, and a mismatch occurs with a spot size (for example, approximately several μm to 10 μm) of general external light. Therefore, high coupling loss occurs.
Thus, a technology is available wherein a mismatch with the spot size of external light is eliminated to reduce the coupling loss by providing a core with a taper portion having a core width that decreases toward an end face of the core to or from which light is inputted or outputted thereby to increase the spot size.